The FBI said the man behind the mass shooting in Las Vegas has no connections to ISIS despite the group's claim they were behind the attack.
ISIS said the perpetrator was "a soldier" who had converted to Islam months ago, without providing any evidence to support the claim.
The group's Aamaq news agency released two brief statements hours after the shooting at a country music concert that killed at least 50 people and wounded at least 400. It was the deadliest mass shooting in modern U.S. history.
IS did not name the suspected shooter, but said he had "executed the operation in response to calls to target countries of the coalition" batting the extremist group in Iraq and Syria.
Police have identified the shooter as Stephen Craig Paddock, 64, of Mesquite, Nevada, and have said he killed himself after the shooting. Sheriff Joseph Lombardo said authorities believe it was a "lone wolf" attack, and the U.S. Homeland Security Department said there was no "specific credible threat" involving other public venues in the U.S.
The IS group often claims attacks by individuals inspired by its message but with no known links to the group. However, it is not known to have claimed any attacks that were not at least loosely linked to it.
Before Sunday, the deadliest mass shooting in modern U.S. history took place in June 2016, when a gunman opened fire at a gay nightclub in Orlando, Florida, killing 49 people. The gunman, Omar Mateen, had pledged allegiance to IS and it claimed the attack.
The extremist organization has suffered a string of major setbacks in Iraq and Syria, where it has lost much of the territory it once claimed as part of a self-styled Islamic caliphate. However, the group remains active in recruiting followers on social media, and has repeatedly called for attacks in Western nations.